Adjustable voltage autotransformer



United States Patent ADJUSTABLE VOLTAGE AUTOTRANSFORMER Arthur E.Snowdon, Philmore E. Johnson, Elmer W.

Madsen, and George A. Page, Jr., all of Bristol, Conn.,

assignors to The Superior Electric Company, Bristol,

Conn., a corporation of Connecticut Filed July 7, 1959, Ser. No. 825,4856 Claims. (Cl. 336-148) The present invention relates to an electricalcontrol device for providing an adjustable output voltage and moreparticularly to the type of device known as an autotransformer.

As commonly manufactured, an autotransformer of the type to which theinstant invention is directed includes a coil composed of an annularcore on which a length of wire is toroidally wound to form a winding. Aperipheral portion of each of the turns of the winding is formed into acommutating surface on which a brush is movable, being always inengagement with at least one turn. By moving the brush along thewinding, the output voltage may be adjusted.

An object of the present invention is to provide an autotransformer soconstructed and arranged that it can safely control a larger amount ofelectrical current than in heretofore units of the same size.

A further object of the present invention is to provide anautotransformer of the above type which is rugged in construction andless subject to malfunctioning, is composed of relatively few,economically produced parts that are capable of ready fabrication andassembly to form the complete autotransforrner.

A further object of the present invention is to provide a brush andbrush holder unit which enables substitution of a brush simply andeasily and which increases the durability and operation of theautotransformer by stabilizing the brush on the commutating surface onwhich it rides.

In achieving the above objects, the autotransformer of the presentinvention provides for an annular core having a toroidal winding and formounting within the open center of the core a shaft which connects tothe brush to move it on the commutating surface. According to thepresent invention, the shaft and brush arm are press fitted together toform a single assembly whereby the shaft and brush relationship ismaintained constant. In addition, the parts are arranged so that asubstantial portion of the assembly is contained within the center ofthe core thereby enabling an axial-1y longer core to be employed andhence an increase in the rating of the unit without increasing theoverall thickness of the autotransformer.

A further feature of the present invention resides in the brush andbrush holder of the brush arm which enables the brush to be readilyremoved when needed and a new brush substituted. This is accomplished byconstructing the brush and the brush arm to have cooperating portionsand by tensioning the brush arm against the commutating surface to holdthe brush in place and against the commutating surface. Moreover thebrush and the brush holder stabilize the brush on the commutatingsurface to maintain a flat area of the brush thereagainst by preventingmovement of the brush relative to the holder in the path of movement ofthe holder while permitting relative pivotal movement therebetween in aplane perpendicular to the commutating surface to accommodate forunevenness in the commutating surface.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is a side view of the autotransformer of the present inventionshown mounted on a panel, the latter being in section.

FIG. 2 is an end view looking in the direction of the arrows 22 of FIG.1.

3,087,132 Patented Apr. 23, 1963 FIG. 3 is an elevation, somewhatenlarged and partly in section, of the details of the brush actuatingmechanism of the autotransformer of the present invention.

FIG. 4 is an end view of the brush and brush holder forming part of thepresent invention.

FIG. 5 is a top view of the brush of the present invention.

FIG. 6 is a sectional view taken on the line 6--6 of FIG. 5.

FIG. 7 is a detail, looking at the side if the brush and brush holdingportion of the brush arm.

Referring to the drawing, the autotransformer of the present inventionis generally indicated by the reference numeral 10 and has an annularcoil including an annular core 11 preferably formed by spirally windinga length of paramagnetic material, such as iron. A pair of front andrear, annular end caps 12 and 13 abuts the ends of the core while atubular member 14 encompasses the periphery of the core, these membersbeing preferably formed of insulating plastic material. A winding 15,composed of a single length of electrical conducting wire, is toroidallywound about the core over the members 1'2 and 13 in a single layer ofjuxtaposed turns. A commutating surface 16 is formed on the winding asby milling fiat a similar portion of each turn that is present on theraised annular portion 17 of the rear end cap 12.

Positioned against the front end cap 13, opposite the end cap having thecommutating surface, is a circular base 18 having the cross-sectionalshape shown and this base, for reasons hereinafter apparent, is formedof heat conductive, metallic material such as cast aluminum. Anelectrically insulating disk 19', of mica for example, is secured to theback face of the base 18 to be positioned between it and the coil. Acentral aperture 20 is formed in the base and circumscribing theaperture is a larger circular indentation 21.

Positioned against the rear face of the coil is an annular end member 22formed of insulating material such as plastic and having a shape whichforms a hub or cylindrical portion 23, an outwardly extending flange 24and a central, stepped aperture 25 having portions of increasingdiameter terminating at steps 26 and 27. A tubular sleeve 28 extendsthrough the central apertures 20 and 25 and at one end portion has anoutwardly extending flange 29 which abuts the steps 26 formed in theannular member 22, while its other end portion is threaded as at 3%. Anut 31 is threaded onto the portion 29 to fit within the indentation 21and serves to unitarily clamp the base 18 and annular member 22 againstthe coil. To prevent rotation of the sleeve as the nut is screwedthereon the base 13 has a projection 32 fitting in a hole in the end cap13 and the aperture 20 is keyed to the sleeve as by mating flat portions(not shown).

The present invention provides for the clamping pressure of the base '18and the member 22 to be parallel to and concentric about the axis of thecoil to prevent axial movement of the laminations of the core relativeto each other which would cause the end caps to become nonparallel toeach other and at an angle rather than perpendicular to the axis of thecoil. To this end, the base 18 is formed with a thickened annularportion 33 (the thickness occurring as a step in the back thereofbecause the front is flat) and this is the portion that is axiallyaligned with the flange 24 of the member 22 so that axial clampingpressure is exerted on the coil adjacent the center edge portionsthereof. To prevent radial movement of the base and member 22, theformer has an annular hub 34 while the latter has the cylindricalportion 23, both of which extend into the center of the coil inclosefitting engagement therewith.

A shaft 35 is rotatably mounted in the sleeve 28 and at one end portionis formed with a groove 36 in which o is located a C-ring 37 that abutsagainst the end of the sleeve to prevent axial movement in one directionof the shaft. The other end of the shaft is formed with areduceddiameter portion 38 on which is press fitted an insulatingbushing3 formed of plastic material and having the shape shown whichincludes a shank 40 and head 41.

An annular hub 42 having an inwardly extending flange 43 is press fittedonto the shank 40 of the bushing 39 to have the flange 43 abut againstthe head 41 of the bushing 39. A brush arm 44 preferably formed ofelectrical conducting material that is also resilient, such as berylliumcopper, has a collar portion 45 which circumscribes the head 41 and formaintaining the arm secured to the hub 42, both electrically andmechanically, the hub is provided with a peripheral skirt 46 that isspun over onto the collar portion 45 except for an opening 47 in theskirt through which the brush arm extends. The spun-over skirt preventsaxial movement of the arm while the sides of the opening prevent radialmovement thereof relative to the hub. The other end of the brush arm 35carries a brush 48 which will be hereinafter described that rides inelectrical contact on the commutating surface 16. Also circumscribingthe shank 40 of the bushing 39 is a saucer shaped annular spring washer49 formed of resilient, conducting material and an end annular portion56 of a conducting bar 51. The conducting bar 51 terminates in aterminal 52 and a screw 53 threads into an aperture in the rear end cap12 to aid in securing the bar. The annular portion th of the conductorbar is within the stepped aperture 25 and passes through a radial cutout54 in the flange 24.

With the above construction, it will be appreciated that current isconducted from the commutating surface of the winding through the brush48, the brush arm 44, the hub 42, the spring washer 49 to the annularportion 50 of the conducting bar 51 and then to the terminal 52, theseparts being formed of electrical conducting material. In additionconduction of electricity to the shaft 35 is prevented by the parts 2 2and 39 being formed of insulating material.

In the assembly of the autotransformer, the brush arm 44 is positionedon the hub 42 and made fast thereto by spinning over the skirt 46. Theinsulating bushing 39 is then press fitted into the hub 42 and the shaftis press fitted into the insulating bushing. The washer 49 and sleeve 28are then positioned on the shaft and secured in'place by the C-ring 37to form a brush moving assembly. To complete the autotransformer of thepresent invention, the bar 51 and member 22 are placed on the sleeve andthe shaft and sleeve passed through the center of the coil to havepositioned thereon the base 18 and the nut 31 which is threaded to clampthe parts together. The screw 53 is threaded into the rear end cap 12 tohold the conducting bar 51 against movement while the slot 54 formed inthe flange also aids in restraining movement of the bar. With thisstructure, manufacturing tolerances can be absorbed because the springwasher 49 in addition to conducting current between the hub 42 and thebar 51 also serves to tension rearwardly the shaft by causing the bar 51to abut the step 27 formed in the member 22 while pushing against thehub 42 thereby forcing the C-washer against the end of the sleeve.

The brush 48, as shown in FIGS. 4, 5 and 6, includes an elongate carbonpart 55 having one side beveled into a tip 56 having a fiat rectangularsurface. The other sides 57 are rectilinear and flat and are secured ina rectangular cutout 58 formed in a block 59 of conducting material, asby soldering or brazing. The block 59 is of single-piece constructionand includes a raised center section 60 of rectangular configurationwhich fits within a rectangular aperture 61 formed in the brush arm 44with the sides of the aperture transverse to the length of the brush armabutting the adjacent sides of the section 60 to prevent relativemovement therebetween tangential to the commutating. surface. The brusharm has an inwardly directed lip 62 on the back side of the aperture 61and another inturned lip 63 formed on the front side. On either side ofthe aperture 61, the brush arm is formed to have oppositely disposed andaligned wing portions 64 and 65 each having a ridge 66 and 67respectively with each ridge being arcuate in cross-section, as shown,and being approximately as long as the width of the aperture 50. Theridges engage flat rectangular surfaces 68 and 69 located below and atthe sides of the raised section 66 and oppositely disposed on eitherside of the riding surface tip 56.

With the above construction of the brush and brush arm, it will beappreciated that the only pressure holding the brush in place is thatexerted by the brush arm as it is tensioned by itself towards thecommutating sur-' face with the brush positioned therebetween, the brusharm in its at rest position not lying in a single plane since it is bentat the line 70 and if a brush were present, the brush arm Would engagethe outer periphery of the flange 24. If desired to remove the brush allthat is required is the removal of the tension of the brush arm bybending it awayfrom the commutating surface and letting the brush fallfreely from the arm. A reversal of this procedure will enable thepositioning of the brush in place. The brush arm is of substantial widthand therefore has substantial resistance to twisting.

The tip 56 of the brush provides for a substantial flat area of contactwith the commutating surface without on gaging an undesirable number ofturns and the present invention provides for maintaining the flat areaof the brush completely in contact with the commutating surface, eventhough there may be irregularities in the flatness of the commutatingsurface. While theoretically it is desirable to have the commutatingsurface flat and in a single radial plane, it has been found that duringmanufacture the surface formed is not exactly flat but has portions thatare flat yet at an angle to the radial plane. In order to compensate forvariations, the brush and brush holder of the present invention preventsthe brush from moving relative to the brush arm in the path that thebrush arm moves and yet be permitted to move freely perpendicular to thepath. This is, accomplished by the ridges 66 and 67 each being of alength and extending substantially along the path of movement of thebrush which prevents pivotal movement of the brush in the brush armabout the tip 56. However in order to compensate for the commutatingsurface not completely lying in a radial plane, the flat surfaces 68 and69 of the brush are engaged only by the ridges 66 and 67 enabling it tobe easily pivoted about the ridge for movement perpendicular to thebrush path. Thus the brush and brush holder provide for prevention ofmovement along the commutating surface but yet provide for pivotalmovement in a plane radial to the commutating surface there bystabilizing the brush and maintaining substantial contact with thecommutating surface by keeping the flat tip 56 completely in engagementthereto.

As shown in FIG. 1, the autotransformer 10 as illustrated is mounted onthe back of a panel 71 having an aperture 72 through which part of thethreaded portion 30 of the sleeve extends. A nut 73 threads on theportion to clamp the outer face of the circular base 18 against theinside surface of the panel. A knob 74 is mounted on the end of theshaft and in addition a dial 75 may be employed and preferably held inplace by the nut 73. In order to facilitate connections to the device,there are provided three terminals 76 having the shape shown and securedto the peripheral covering 14 by staples 77 having bent over endsthough, of course, other methods of securement may be employed, ifdesiderd. Not shown are connections between two of the terminals and theends of the winding, the other terminal being connected if desired to atap intermediate the ends of the winding.

The conducting bar 51 is provided with a pair of outturned stops 78which are engageable by the brush arm to prevent the brush from engagingthe coil where there is no commutating surface.

It will accordingly be appreciated that there has been disclosed anautotransformer in which the shaft and brush arm assembly are composedof relatively few, easily manufactured parts that may be economically,if not automatically, assembled and which may then be easily assembledto the other parts of the autotransformer to fabricate it. The partsenable an increase of rating of the autotransformer unit without anincrease in the thickness thereof by having substantial portions of theshaft and brush assembly recessed Within the center in the core whichenables a thicker core to be employed. The increased rating producesmore heat during use, however this heat is dissipated with a substantialrise in the autotransformer by it passing to the heat conductingcircular base 16 which acts as a radiator and may dissipate the heat byconvection and/or conduction to the mounting panel.

Moreover the present invention facilitates interchangeability of thebrush from the brush arm quickly and easily without disassembling anyparts and yet provides for a brush that is stabilized and maintains aflat area of contact with the commutating surface.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

We claim:

*1. An adjustable voltage autotransformer comprising an annular coilincluding an annular core of paramagnetic material and a toroidalwinding encircling said core and formed with an arcuate commutatingsurface on one end thereof, a base formed with a central aperture andpositioned against the other end surface of the coil, an annular endmember of insulating material and formed to have an outwardly extendingflange and a hub portion formed with a stepped aperture, said memberbeing positioned with its flange against the one end surface of the coiland its hub portion within the center of the coil, means clamping thebase and annular member to the coil, a shaft extending through thecenter of the coil and apertures in the base and member and having oneend terminating in the stepped aperture, an insulating bushing securedon the end of the shaft Within the aperture, a conducting elementincluding a brush arm secured on the bushing, a brush on the end of thearm and adapted to ride in electrical engagement with the commutatingsurface, a conducting bar having a portion recessed within the steppedaperture encircling the bushing, and a conducting means on the bushingwithin the stepped aperture positioned between the conducting bar andthe conducting element in electrical engagement therewith whereby theconnections to the shaft, brush arm and conducting bar are substantiallyrecessed within the annular member.

2. An adjustable voltage autotransformer comprising an annular coilincluding an annular core of paramagnetic material and a toroidalwinding encircling said core and formed with an acruate commutatingsurface on one end thereof, a base formed with a central aperture andpositioned against the other end surface of the coil, an annular endmember of insulating material and formed to have an outwardly extendingflange formed with a radial cutout and a hub portion formed with astepped aperture, said member being positioned with its flange againstthe one end surface of the coil and its hub portion within the center ofthe coil, means clamping the base and annular member to the coil, ashaft extending through the center of the coil and apertures in the baseand member and having one end terminating in the stepped aperture, aninsulating bushing secured on the end of the shaft within the aperture,a conducting element including a brush arm secured on the bushing, abrush on the end of the arm and adapted to ride in electrical engagementwith the commutating surface, a conducting bar having a portion recessedwithin the stepped aperture encircling the bushing and having a flatportion extending through the radial cutout and constituting a terminal,and a conducting means on the bushing within the stepped aperturepositioned between the conducting bar and the conducting element inelectrical engagement therewith whereby the connections to the shaft,brush arm and conducting bar are substantially recessed within theannular member.

3. An adjustable voltage autotransformer comprising an annular coilincluding an annular core of paramagnetic material and a toroidalwinding encircling said core for a substantial portion thereof andformed with an arcuate commutating surface on one end thereof, a baseformed with a central aperture and positioned against the other endsurface of the coil, an annular end member of insulating material andformed to have an outwardly extending flange formed with a radial cutoutand a hub portion formed with a stepped aperture, said member beingpositioned with its flange against the one end surface of the coil andits hub portion within the center of the coil, a sleeve extendingthrough the center of the coil and having one end positioned against thestepped aperture and its other end portion threaded and extending intoand beyond the aperture in the base, a nut threaded on the end portionto clamp the coil between the member and the base, a shaft rotatablymounted in the sleeve and having one end portion extending beyond thebase to provide a manipulatable portion, means on the shaft at the endportion thereof extending beyond the base abutting the end of thesleeve, the other end of the shaft terminating within the steppedaperture, an insulating bushing secured on the other end of the shaft, aconducting element including a brush arm secured on the bushing, a brushon the end of the arm and adapted to ride in engagement with thecommutating surface, a conducting bar having a portion encircling thebushing within the stepped aperture and having an annular portionabutting a step of the annular member and a flat portion extendingthrough the radial cutout and constituting a terminal, and a conductingmeans encircling the bushing within the stepped aperture and positionedbetween the conducting bar and the conducting element to be inelectrical engagement therewith, whereby rotation of the shaft enablescurrent to be conducted from the brush through the conducting elementand the spring to the terminal portion of the conducting bar.

4. An adjustable voltage autotransformer comprising an annular coilincluding an annular core of paramagnetic material and a toroidalwinding encircling said core and formed with an arcuate commutatingsurface on one end thereof, a base formed with a central aperture andpositioned against the other end surface of the coil, an annular endmember of insulating material and formed to have an outwardly extendingflange and a hub portion formed with a stepped aperture, said memberbeing positioned with its flange against the one end surface of the coiland its hub portion within the center of the coil, means clamping thebase and annular member to the coil, a shaft extending through thecenter of the coil and apertures in the base and member and having anend terminating in the stepped aperture, an insulating bushing securedon the end of the shaft within the aperture, a conducting elementincluding a brush arm secured on the bushing, said brush arm beingelongate and having at its end substantially flat and aligned oppositelydisposed wing portions, a brush including a portion adapted to ride onthe commutating surface, and a pair of conducting surfaces oppositelydisposed about the portion, the conducting surfaces and the wingportions being in engagement one to one and the contacting surfacesbeing formed to have contact with each other to enable the brush to befreely pivotable about an axis transverse to the brush arm and abuttingmeans for preventing relative movement between the brush and brush armtransverse to the length of the brush arm, a conducting bar having aportion recessed within the stepped aperture encircling the bushing, anda conducting means on the bushing within the stepped aperture positionedbetween the conducting bar and the conducting element in electricalengagement therewith.

5. An adjustable voltage autotransformer comprising an annular coilincluding an annular core of paramagnetic material and a toroidalwinding encircling said core and formed with an arcuate commutatingsurface on one end thereof, a base formed with a central aperture andpositioned against the other end surface of the coil, an annular endmember of insulating material and formed to have an outwardly extendingflange and a hub portion formed with a stepped aperture, said memberbeing positioned with its flange against the one end surface of the coiland its hub portion within the center of the coil, means clamping thebase and annular member to the coil, a shaft extending through thecenter of the coil and apertures in the base and member and having anend terminating in the stepped aperture, an insulating bushing securedon the end of the shaft within the aperture, a conducting elementincluding a brush arm secured on the bushing, a brush on the end of thearm and having a carbon portion formed with a riding surface adapted toride on the commutating surface, a pair of conducting surfaces aligned,elevated above and oppositely disposed about the riding surface, aconducting bar having a portion recessed within the stepped apertureencircling the bushing, and a conducting means on the bushing within thestepped aperture positioned between the conducting bar and theconducting element in electrical engagement therewith.

6. An adjustable voltage autotransformer comprising an annular coilhaving an annular core of paramagnetic material and a toroidal windingencircling said core and having an arcuate commutating surface formed onone end surface of the coil, a base formed with a central aperture andpositioned against the other end surface of the coil, an annular endmember of insulating material and formed to have an outwardly extendingflange and a central stepped aperture and a hub portion, said memberbeing positioned with its flange against the one end surface of the coiland its hub portion recessed within the center of the coil, a sleeveextending through the center of the coil and having one end abuttingagainst the stepped aperture and its other end portion threaded andextending into and beyond the aperture in the base, and a nut threadedon the end portion to clamp the coil between the member and the base,the flange engaging the coil only on an annular portion adjacent thecenter thereof on the one end surface and the base engaging the coil atthe opposite end surface thereof only at an annular portion adjacent thecenter of the coil thereby clamping the coil axially thereof, said basebeing circular and having a diameter approximating the diameter of thecoil and being formed of heat conducting metal to have. a hub portionprotruding from its inner surface positioned within the recess in thecenter of the coil and having an annular thickened part adjacent the hubportion engaging the end surface of the coil to thereby form an air gapbetween the rest of the end surface of the coil and the base, the outerface of the base being substantially flat and adapted to be mountedagainst a flat surface to conduct heat away from the coil.

References Cited in the file of this patent UNITED STATES PATENTS2,009,013 Karplus July 23, 1935 2,089,434 Schermerhorn Aug. 10, 19372,245,266 Eitrnan June 10, 1941 2,266,532 Braunschweig Dec. 16, 19412,814,023 Alexy Nov. 19, 1957 FOREIGN PATENTS 23,170 Great Britain 1893OTHER REFERENCES Variac, 1955 Bulletin N, page 2, received in library onJanuary 31, 1955.

1. AN ADJUSTABLE VOLTAGE AUTOTRANSFORMER COMPRISING AN ANNULAR COILINCLUDING AN ANNULAR CORE OF PARAMAGNETIC MATERIAL AND A TOROIDALWINDING ENCIRCLING SAID CORE AND FORMED WITH AN ARCUATE COMMUTATINGSURFACE ON ONE END THEREOF, A BASE FORMED WITH A CENTRAL APERTURE ANDPOSITIONED AGAINST THE OTHER END SURFACE OF THE COIL, AN ANNULAR ENDMEMBER OF INSULATING MATERIAL AND FORMED TO HAVE AN OUTWARDLY EXTENDINGFLANGE AND A HUB PORTION FORMED WITH A STEPPED APERTURE, SAID MEMBERBEING POSITIONED WITH ITS FLANGE AGAINST THE ONE END SURFACE OF THE COILAND ITS HUB PORTION WITHIN THE CENTER OF THE COIL, MEANS CLAMPING THEBASE AND ANNULAR MEMBER TO THE COIL, A SHAFT EXTENDING THROUGH THECENTER OF THE COIL AND APERTURES IN THE BASE AND MEMBER AND HAVING ONEEND TERMINATING IN THE STEPPED APERTURE, AN INSULATING